Heat exchanger

ABSTRACT

A heat exchanger that is applicable to a pump and a system where a plurality of tubular elements or cores, each comprising a support cylinder or half-cylinder and at least one curved heat exchange plate. Each plate separating a first cavity from a second cavity where the first cavity contains a liquid and the second cavity receiving a coolant causing the thermal expansion or contraction of the plate. The heat exchanger according to the invention makes it possible to withstand high mechanical stresses. This design makes it better to withstand high pressures despite a large diameter of the cylindrical heat exchange plates without an increase to the thickness of these plates. The pressure being exerted on the tubular elements is primarily radially, more particularly from the outside to the inside for the thinnest cylindrical heat exchange plate in contact with the cavity containing cold coolant or air.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of French Application 06794262.3files Aug. 2, 2006 and published as WO2006FR01870 the entire contents ofwhich is hereby expressly incorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat exchanger used to produce aliquid under pressure by expanding, particularly inside a pump.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 1.98

A hydraulic pump and a hydraulic system incorporating such a pump isknown in the prior art, particularly from the patent applications FR-A-2851 796 and WO-A-2004/079194.

The hydraulic system comprises a hydraulic pump, a hydraulic fluidreservoir and a hydraulic motor.

The hydraulic pump comprises at least one pumping piston and a drivepiston constituted by two stages of the same differential piston. Thepumping piston delimits a pumping chamber inside a pumping cylinder andthe drive piston delimits a drive chamber inside a drive cylinder. Thepumping piston and the drive piston are connected to each other bykinematic connecting means in such a way that an increase in the volumeof the drive chamber corresponds to a decrease in the volume of thepumping chamber and vice versa.

The pumping chamber is hydraulically connected to the system's hydraulicfluid reservoir and to the system's hydraulic motor, which is powered bythe hydraulic pump.

The drive chamber of the pump is hydraulically connected to a tubularheat exchange bundle. A liquid with a high thermal expansion coefficientis present in the drive chamber and the tubular heat exchange bundle.This liquid with a high thermal expansion coefficient is alternatelyplaced in a heat exchange relationship with a hot source and with a coldsource.

Thus, the liquid with a high thermal expansion coefficient isalternately subjected to thermal expansions and thermal contractions,which respectively increase the volume of the drive chamber whiledecreasing that of the pumping chamber, thus forcing the hydraulic fluidinto the hydraulic motor then into the system's reservoir, or decreasethe volume of the drive chamber, thus causing the intake of thehydraulic fluid from the system's reservoir. A pumping effect is thusobtained by the alternating hydraulic fluid discharge and intakemovements.

The tubular heat exchange bundle is constituted by a bundle of verticaltubes closed at their lower end and communicating with each other attheir upper end via a collector into which opens a conduit that connectsto the drive chamber.

The tubular heat exchange bundle is placed inside an enclosure dividedby a horizontal partition. This thermally insulating partition ispierced with holes, thus allowing each tube to pass through thepartition from one side to the other while maintaining as goodimpermeability between the partition and the tubes.

The enclosure is thus divided into a lower chamber comprising acirculating cold coolant and an upper chamber comprising a circulatinghot coolant.

The tubular heat exchange bundle is thus alternately placed in a heatexchange relationship with the cold coolant and with the hot coolant bymeans of an up-and-down movement inside the enclosure. This up-and-downmovement is produced by a jackscrew.

What is needed is a heat exchanger to eliminate the alternating thermalexpansions and contractions to which the fluid with a high thermalexpansion coefficient is subjected result in alternating expansions andcontractions of the tubular heat exchange bundle, which has a tendencyto stretch each tube, eventually causing fatigue in the tubesconstituting the tubular bundle.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention is therefore to propose a heatexchanger that makes it possible to withstand high mechanical stressesfor a long time.

This object is achieved by a heat exchanger comprising a plurality oftubular elements or cores, each comprising: a supporting cylinder orhalf-cylinder, at least one curved heat exchange plate, each plateseparating a first cavity from a second cavity, the first cavitycontaining a liquid and the second cavity receiving a coolant whichcauses the thermal expansion or contraction of the plate and thus,respectively, the compression or expansion of the liquid in the firstcavity an outer retaining tube or half-tube.

According to another feature, the liquid has a high thermal expansioncoefficient.

According to another feature, the outer retaining tube or half-tube, theheat exchange plate or plates, and the supporting cylinder orhalf-cylinder have decreasing diameters.

According to another feature, the first and second cavities aredelimited, on one side, by one of the heat exchange plates, and on theother side by the supporting cylinder or half-cylinder or the outerretaining tube or half-tube, the heat exchange plate(s), the supportingcylinder or half-cylinder and the outer retaining tube or half-tubebeing concentric.

According to another feature, each tubular element is closed at each ofits ends by a flange, one of said flanges being adapted so as to allowthe circulation of the liquid through the flange, the other flangepreventing this circulation.

According to another feature, each tubular element is closed at each ofits ends by a flange, at least one of said flanges being adapted so asto allow the circulation of the coolant or coolants through the flange.

According to another feature, said flanges are adapted so as to allowthe alternating circulation of a coolant heated by a hot source and acoolant cooled by a cold source.

According to another feature, one of the heat exchange plates isequipped with a plurality of first fins in contact with the liquid.

According to another feature, one of the heat exchange plates isequipped with a plurality of first fins in contact with a coolant.

According to another feature, one of the heat exchange plates isequipped with a plurality of second fins in contact with a coolant.

According to another feature, the various tubular elements are parallelto each other.

According to another feature, the various tubular elements are heldtogether by means of straps, each clamping a tubular element andattached to a threaded rod located between at least two tubularelements.

According to another feature, the various tubular elements are heldtogether by means of straps, each clamping a tubular element and weldedto each other.

According to another feature, the various tubular elements are heldtogether by means of straps, each clamping a tubular element andsoldered to each other.

According to another feature, each tubular element or core alsocomprises coolant conduits and spray nozzles adapted for spraying thecoolant from the coolant conduits onto the heat exchange plate.

The invention also relates to a pump comprising: a pumping pistonadapted for actuating a control means via the movement of a fluid, adrive piston connected by kinematic means to the pumping piston andadapted to being actuated by a movement of the liquid of the heatexchanger described above, a hot source and a cold source.

According to another feature, the pump also comprises a bypass adaptedfor alternately feeding a coolant heated under pressure by the hotsource and a coolant cooled at atmospheric pressure by the cold sourceinto the tubular elements or cores of the heat exchanger.

The invention also relates to a system comprising: the pump describedabove, a fluid reservoir and a control means.

Various objects, features, aspects, and advantages of the presentinvention will become more apparent from the following detaileddescription of preferred embodiments of the invention, along with theaccompanying drawings in which like numerals represent like components.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Other features and advantages of the invention will emerge through thereading of the following detailed description of embodiments of theinvention given merely as examples and in reference to the drawings,which show:

FIG. 1, a perspective view of a tubular element of the heat exchangeraccording to a first embodiment of the invention;

FIG. 2, a cross-sectional view of the heat exchanger according to asecond embodiment of the invention;

FIG. 3, a longitudinal sectional view of the heat exchanger according toa third embodiment of the invention;

FIG. 4, a cross-sectional view of the heat exchanger according to afourth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The identical references in the various figures designate similar orequivalent elements.

The heat exchanger according to the invention comprises a plurality oftubular elements. Each tubular element comprises a supporting cylinder,at least one curved heat exchange plate separating a first cavity from asecond cavity, and an outer retaining tube. The first cavity contains aliquid and the second cavity receives a coolant which causes the thermalexpansion or contraction of the plate, and thus the compression orexpansion of the liquid of the first cavity.

The heat exchange plate expands or contracts through contact with thecoolant as a function of the temperature of the coolant or coolantscirculating through the heat exchanger, thus causing a compression orexpansion of the first cavity and hence of the liquid contained in thatfirst cavity.

The supporting cylinder and the outer retaining tube, which are composedof materials which are highly pressure resistant and can be poor thermalconductors, that make it possible to considerably limit the longitudinalexpansion of the heat exchanger and thus to withstand high mechanicalstresses longer than with the tubular heat exchange bundle known in theprior art.

FIG. 1 represents a perspective view of a tubular element of the heatexchanger according to a first embodiment of the invention. The heatexchanger comprises a plurality of tubular elements. In this firstembodiment of the invention, each tubular element 1 comprises an outerretaining tube 6 containing two heat exchange plates 3C, 3F,respectively called the outer plate and the inner plate, whichthemselves contain a supporting cylinder 2. In this embodiment, the heatexchange plates 3C, 3F are cylindrical. It is also possible to conceiveof other embodiments with one or more heat exchange plates which arecurved but not cylindrical, or which form only a portion of a cylinder.The supporting cylinder 2 is for example a solid cylinder. The outerretaining tube 6, the two heat exchange plates 3C, 3F and the supportingcylinder 2 are substantially concentric.

A first cavity, formed between the two heat exchange plates 3C, 3F,contains a liquid 4. Preferably, the liquid 4 has a high thermalexpansion coefficient. The heat exchange plates allow a heat exchangebetween the coolant and the liquid 4. Thus, the liquid 4 expands orcontracts as a function of the temperature of the coolant or coolantscirculating through the heat exchanger, which causes the thermalexpansion or contraction of the liquid 4. The compression or expansioncreated is even greater when the liquid does not have a high thermalexpansion coefficient and when the compression or expansion of theliquid 4 is merely due to the thermal expansion or contraction of theheat exchange plates.

There are two other cavities formed between one of the plates 3C and theouter retaining tube 6 and between the other plate 3F and the supportingcylinder 2, respectively receive a hot coolant 5C and a cold coolant 5Fin the liquid state.

One of the objects of the heat exchanger according to the invention isto compress or expand the liquid 4 by means of a heat exchange betweenthe plates and the coolants 5C, 5F, with the liquid neverthelessremaining constantly in the liquid state. In order to optimize this heatexchange, particularly in terms of duration, these plates 3C, 3F aremade of a material having very good thermal conductivity, i.e. a metal.This also allows a good heat exchange with the liquid 4, which isparticularly important when the liquid 4 has a high thermal expansioncoefficient.

In order for the heat exchanger to better resist fatigue, the outerretaining tube 6 and the supporting cylinder 2 are composed of highlypressure-resistant materials. Thus, to give a non-limiting example, theyare made of carbon composite or filament-wound material or glass. Thesematerials also offer the advantage of having poor thermal conductivity(for example between 0.034 W/mK and 0.045 W/mK), thus also making itpossible to considerably limit heat losses to the outside of the heatexchanger. When not using a liquid with a high thermal expansioncoefficient, heat losses can be limited by the use of a liquid havingpoor thermal conductivity. High pressures are exerted, particularly onthe heat exchange plate in contact with the hot coolant 5C. This platehas a small thickness, typically between several tenths of a millimeterand several millimeters, depending on the nature of the metalconstituting the plate and the size of the exchanger as a function ofthe application. Thus, the speed of the heat exchange is increased, butwithout weakening the plate, since the pressure is exerted on itprimarily radially during expansion (and preferably toward the inside ofthe tubular element), as opposed to primarily longitudinally as in theprior art.

Thus, unlike the tubular heat exchange bundle known in the prior art,the heat exchanger according to the present invention makes it possibleto use heat exchange plates of larger diameter for the same thickness,which are much more resistant to higher pressures, making it possible tobroaden the applications. The diameter of the plates can be increasedwith a constant thickness, either because the pressure is exerted fromthe outside inward and not from the inside outward, or because theplates' resistance to mechanical stresses is facilitated by the outerretaining tube 6 or the supporting cylinder 2, which are made of highpressure-resistant material. If the outer retaining tube 6 or thesupporting cylinder is metallic, it is necessary to protect them fromheat in order to prevent them from expanding, which would reduce theefficiency of the system. It is therefore conceivable to cool theoutside of the retaining tube with the fluid 5F_(f).

In a variant of embodiment, the outer retaining tube 6 and thesupporting cylinder 2 are both made of metal, but the tubular elementcomprises at each of its ends a flange which is welded or soldered tothe tube in order to allow these two elements 2, 6 to withstand highpressures.

Preferably, the hot coolant 5C is contained between the outer retainingtube 6 and the outer heat exchange plate 3C, while the cold coolant 5Fis contained between the inner heat exchange plate 3F and the supportingcylinder 2.

Thus, when the heat exchange plate 3C is expanded, the heat exchangeplate 3F will be subjected to radial compression stress. The presence ofthe supporting cylinder 2 makes it possible to help said inner heatexchange plate 3F withstand this compression stress, which is exerted onthe tubular element radially in the direction of the supporting cylinder2.

The inner heat exchange plate 3F also comprises a plurality of firstlongitudinal fins 31 located inside the cavity containing the coldcoolant 5F. These first fins 31 make it possible to more easilywithstand the radial compression stresses exerted on the tubular elementas a result of the expansion of the outer heat exchange plate 3C. Thesefirst fins also serve to position the supporting cylinder 2substantially at the center of the inner plate 3 _(F).

The outer heat exchange plate 3C also comprises a plurality of secondlongitudinal fins 32 located inside the cavity containing the hotcoolant 5 _(c). These second fins 32 serve, in particular, to positionthe outer plate 3C substantially at the center of the retaining tube 6.

Take the example in which the plates 3C and 3F are made of steel, theplate 3C has for example a thickness of 3 mm and the plate 3F has athickness of 1 mm. The plate 3C can then sustain a pressure of 400 barwith the help of the outer retaining tube 6. The plate 3F can sustainthe same pressure as the plate 3C despite its smaller thickness becausethe pressure is exerted from the outside inward.

The cylindrical heat exchange plate 3 _(f) is alternately in contactwith the cold coolant 5F coming from the cold source, and with air whenthe flow of cold coolant 5F is stopped.

FIG. 2 represents a cross-sectional view of the heat exchanger accordingto a second embodiment of the invention. In this second embodiment, theheat exchanger comprises a plurality of tubular elements 1. Each tubularelement 1 comprises an outer retaining tube 6 containing a single heatexchange plate 3, which itself contains a supporting cylinder 2. In thisembodiment as well, the heat exchange plate 3 is, non-limitingly,cylindrical. The supporting cylinder 2 is for example a solid cylinder.The outer retaining tube 6, the heat exchange plate 3 and the supportingcylinder 2 are substantially concentric.

A first cavity is formed between the heat exchange plate 3 and the outerretaining tube 6, and a second cavity is formed between the heatexchange plate 3 and the supporting cylinder 2. One of these cavitiesreceives a liquid 4 while the other cavity receives a coolant 5. Theliquid 4 has, for example, a high thermal expansion coefficient. Ittherefore enables a greater compression of the liquid compared to theexpansion of the heat exchange plate alone, as explained above.

As explained above, the heat exchange plate 3 is made of a materialhaving very good thermal conductivity, i.e. of metal, in order tooptimize the heat exchange.

Likewise, as explained above, the outer retaining tube 6 and thesupporting cylinder 2 are composed of high pressure-resistant materialshaving poor thermal conductivity, such as, for example, a compositecarbon or filament-wound material or glass.

In this embodiment, hot and cold coolant 5 is alternately injected intothe cavity provided for receiving said fluid.

Preferably, the liquid 4 is contained between the outer retaining tube 6and the heat exchange plate 3, while the coolant 5 is contained betweenthe heat exchange plate 3 and the supporting cylinder 2.

Thus, when the heat exchange plate is expanded, it will be subjected toradial compression stress. The presence of the supporting cylinder 2makes it possible to help the heat exchange plate 3 withstand thiscompression stress, which is exerted in a plane transverse to thetubular element in the direction of said supporting cylinder 2.

The heat exchange plate 3 also comprises a plurality of firstlongitudinal fins 31 located inside the cavity containing the liquid 4.These first fins 31 make it possible to increase the heat exchangesurface.

The heat exchange plate 3 also comprises a plurality of secondlongitudinal fins 32 located inside the cavity containing the coolant 5.These second fins 32 serve both to position the supporting cylinder 2substantially at the center of the plate 3 and to more easily withstandthe substantial deformations that might result from the compressionstresses exerted transverse to the tubular element as a result of theexpansion of the plate 3.

As illustrated in FIG. 2, the tubular elements are substantiallyparallel to each other, and preferably vertical. They are preferablydisposed in contact with each other so as to limit energy losses, andfor example so that their axes form trihedral. This arrangement of thetubular elements, and the manner in which they are attached as describedbelow, can also be applied to the tubular elements 1 according to thefirst and third embodiments of the invention.

Each tubular element 1 is clamped by a strap, not shown, which isattached to a threaded rod 7 located at the center of the trihedral.

In order to make the heat exchanger more durable, the array of tubularelements 1 is held together by a synthetic resin.

In a variant of embodiment, the straps are welded or soldered to eachother.

In addition, each tubular element 1 is closed at each of its ends by aflange, not shown. Only one of said flanges needs to allow the liquid 4to be circulated through said flange. In particular, the flanges adaptedfor circulating the liquid 4 must all be disposed on the same side ofthe various tubular elements constituting the heat exchanger.

On the other hand, it is possible for one or both of the two flanges toallow the coolant 5 to circulate through this or these flange(s).

FIG. 3 represents a longitudinal sectional view of the heat exchangeraccording to a third embodiment of the invention.

In this third embodiment, the heat exchanger comprises a plurality oftubular elements 1. Each tubular element 1 comprises an outer retainingtube 6 containing a single heat exchange plate 3, which itself containsa supporting cylinder 2. In this embodiment as well, the heat exchangeplate 3 is vertical and, non-limitingly, cylindrical. The supportingcylinder 2 is for example a solid cylinder. The outer retaining tube 6,the heat exchange plate 3 and the supporting cylinder 2 aresubstantially concentric.

A first cavity is formed between the heat exchange plate 3 and the outerretaining tube 6, and a second cavity is formed between the heatexchange plate 3 and the supporting cylinder 2. One of these cavitiesreceives a liquid 4, while the other cavity receives a coolant 5. Theliquid 4 has for example a high thermal expansion coefficient. Ittherefore enables greater compression of the liquid compared to theexpansion of the heat exchange plate alone, as explained above.

As explained above, the heat exchange plate 3 is made of a materialhaving very good thermal conductivity, i.e. of metal, in order tooptimize the heat exchange.

Preferably, the liquid 4 is contained between the outer retraining tube6 and the heat exchange plate 3, while the coolant 5 is received betweenthe heat exchange plate 3 and the supporting cylinder 2.

Thus, when the heat exchange plate 3 is expanded, it will be subjectedto radial compression stress. The presence of the supporting cylinder 2makes it possible to help the heat exchange plate 3 withstand thiscompression stress, which is exerted in a plane transverse to thetubular element in the direction of said supporting cylinder 2.

The heat exchanger also comprises, between the supporting cylinder 2 andthe cavity containing the coolant 5, two conduits 8, 9 which feed thehot or cold coolant from the hot or cold source into the heat exchanger.These conduits are thermally insulated from each other by a firstseparator 10 and are thermally insulated from the cavity containing thecoolant by a second separator 11. The separators are made of a materialwith very low thermal conductivity, in order to avoid heat losses.

Spray nozzles 12, 13 make it possible to spray the hot or cold coolantthrough capillary tubes running through the separators 10, 11 from theconduits 8, 9 to the cavity, which is initially filled with air and isintended to contain the hot or cold coolant 5. These capillary tubesmake it possible, at atmospheric pressure, to stop the coolantsprecisely at the outlet port when they are liquids, and to reduce thetime it takes the coolants to go from the control valves to the heatexchange plate 3. This spraying is substantially radial and allows for afast and complete spraying of the heat exchange plate 3.

FIG. 4 represents a cross-sectional view of the heat exchanger accordingto a fourth embodiment of the invention.

In this fourth embodiment, the heat exchanger comprises a plurality ofcores 101. Each core 101 comprises two elements 107, which aresymmetrical to each other. The two elements 107 are impermeably joinedto each other at a joint 100. Each core 101 comprises two retaininghalf-tubes 106 oriented with their concave side toward the outside ofthe core. The two half-tubes 106 therefore have their backs to eachother. Each retaining half-tube 106 contains a heat exchange plate 103,which itself contains a supporting half-cylinder 102. In thisembodiment, the heat exchange plate 103 that is semi-cylindrical. Theheat exchange plate 103 is inserted so as to rest against a shoulder 114inside a retaining half-tube 106 and is held against this shoulder by aretaining means, for example a weld 115.

A first cavity is formed between the heat exchange plate 103 and theretaining half-tube, and a second cavity is formed between the heatexchange plate 103 and the supporting half-cylinder 102. One of thesecavities receives a liquid 104 while the other cavity receives a coolant105. The liquid 104 has, for example, a high thermal expansioncoefficient. It therefore enables a greater compression of the liquidcompared to the expansion of the heat exchange plate alone, as explainedabove.

As explained above, the heat exchange plate is made of a material havingvery high thermal conductivity, i.e. of metal, in order to optimize theheat exchange.

Preferably, the liquid 104 is contained between the retaining half-tubeand the heat exchange plate 103, while the coolant 105 is sprayed ontothe heat exchange plate 103 by a spray device contained in thesupporting half-cylinder 102.

Thus, when the heat exchange plate 103 is expanded, it will be subjectedto radial compression stress. The presence of the supportinghalf-cylinder 102, as well as the shape of the exchange plate 103, makesit possible to help this exchange plate 103 withstand the compressionstress, which is exerted in a plane transverse to the tubular element inthe direction of said supporting half-cylinder 102.

The spray device of each supporting half-cylinder 102 comprises twoconduits 108, 109, which feed the hot or cold coolant from the hot orcold source into the heat exchanger. These conduits are thermallyinsulated from each other and are thermally insulated from the cavityreceiving the coolant. Spray nozzles 112, 113 make it possible to spraythe hot or cold coolant from the conduits 108, 109 onto the heatexchange plate 103. This spraying is substantially radial and allows fora fast and complete spraying of the heat exchange plate 103.

It is possible for the perimeter of the heat exchange plate not to becircular or cylindrical. Lobed shapes suggesting a fluted cake mold orarched shapes make it possible to benefit from an increased length ofthe perimeter, thus contributing to a greater linear expansion of theheat exchange plate, and hence to its compressive displacement of theliquid located inside the cavity 104.

In the four embodiments of the invention described above, the coolants5, 5C, 5F are for example water, and the liquid 4 is for exampleethanol. The thermal expansion coefficient of ethanol is 1.1·10⁻³ K⁻¹.

The hot coolant 5C is heated by a cold source and the cold coolant 5F iscooled by a cold source.

The hot source is for example a solar panel. In that case, the flow ofenergy produced by the hot source being low, it is particularlyimportant to reduce heat losses to a minimum in order to conserve theavailable energy.

The heat exchanger according to the invention is intended to beinstalled in a pump which also comprises a pumping piston adapted foractuating a control means via the movement of a fluid (hydraulic liquidor gas), a drive piston connected by kinematic means to the pumpingpiston and adapted to being actuated by a movement of the liquid 4coming from the heat exchanger described above, by a hot source and by acold source.

The pump contains, for example, several heat exchangers.

The pump, in order to operate, also comprises a bypass which makes itpossible to alternately feed a hot coolant heated by the hot source anda cold coolant cooled by the cold source into the tubular elements 1 ofthe heat exchanger in order to create alternating thermal expansions andcontractions, thus making it possible to actuate the drive piston.

The pump according to the invention is intended to be installed in asystem which also comprises a control means, for example a motor, and afluid reservoir.

The system is, for example, an air conditioner. In that case, thepumping chamber takes in and compresses gas and serves as a compressor.The hot source is for example one or more solar panel(s) or anisothermal tank for storing hot coolant, which can be used at night. Thecold source is for example an ornamental pond or a swimming pool.

In a variant, the system is a hydraulic system producing householdelectricity. In that case, the control means is a hydraulic motor. Thehot source is for example one or more solar panel(s) and/or anisothermal tank for storing a coolant, which can be used at night. Thecold source is for example a tank, an ornamental pond or a swimmingpool.

In a variant, the system is a hydraulic system producing householdelectricity from geothermal energy. In that case, the hydraulic pumpoperates a hydraulic motor, which drives an electrical generator. Thehot source in that case is constituted by hot water produced bygeothermal energy, and the cold source is for example constituted by thenatural environment, i.e. hillside runoff, a river, the sea, etc.

When the system comprises a hot source constituted by solar panels, theprevailing pressure in the hot coolant circuit should be relatively highin order to maintain the coolant (for example water) in the liquidstate; part of the pressure generated by the system is used to re-injectthe coolant into the solar panel. Otherwise, the water evaporates. Onthe other hand, the prevailing pressure in the cold coolant circuit canbe the ambient pressure. Thus, in that case, the use of a heat exchangerwith tubular elements according to the first embodiment described aboveis particularly suitable.

1. A heat exchanger comprising: a plurality of tubular elements or cores(1, 101), each having; a supporting cylinder or half-cylinder (2, 102);at least one curved heat exchange plate (3, 3C, 3F, 103), each plateseparating a first cavity from a second cavity, said first cavitycontaining a liquid (4, 104) and said second cavity receiving a coolant(5, 5C, 5F, 105) which causes a thermal expansion or contraction of saidat least one curved heat exchanger plate (3, 3C, 3F, 103) and thus,respectively, a compression or a expansion of said liquid in said firstcavity, and an outer retaining tube or half-tube (6, 106).
 2. The heatexchanger according to claim 1 wherein said liquid (4) has a highthermal expansion coefficient.
 3. The heat exchanger according to claim1 wherein said outer retaining tube or half-tube (6, 106), said heatexchange plate or plates (3, 3C, 3F, 103), and a supporting cylinder orhalf-cylinder (2, 102) have decreasing diameters.
 4. The heat exchangeraccording to claim 3 wherein a first and a second cavities aredelimited, on one side, by one of said heat exchange plates (3, 3C, 3F,103), and on the other side by the supporting cylinder or half-cylinder(2, 102) or the outer retaining tube or half-tube (6, 106), said atleast one curved heat exchanger plate (3, 3C, 3F, 103), said supportingcylinder or half-cylinder (2, 102) and said outer retaining tube orhalf-tube (6, 106) being concentric.
 5. The heat exchanger according toclaim 4 wherein each said tubular elements or cores (1, 101) is closedat each of its ends by a first and a second flange, one of said flangesbeing adapted so as to allow the circulation of the liquid (4) throughsaid first flange and said second flange thereby preventing thiscirculation.
 6. The heat exchanger according to claim 5, wherein each ofsaid plurality of tubular elements or cores (1, 101) is closed at eachof its ends by a first and a second flange, at least one of said flangesbeing adapted so as to allow the circulation of the coolant or coolants(5, 5C, 5F) through said at least one flange.
 7. The heat exchangeraccording to claim 6, wherein said flanges are adapted so as to allowthe alternating circulation of a coolant heated by a hot source and acoolant cooled by a cold source.
 8. The heat exchanger according toclaim 7, wherein said heat exchange plate or plates (3, 3C, 3F, 103) isequipped with a plurality of first fins (31) in contact with said liquid(4, 104).
 9. The heat exchanger according to claim 8, wherein said atleast one curved heat exchanger plate (3, 3C, 3F, 103) is equipped witha plurality of first fins (31) in contact with said coolant (5, 5C, 5F,105).
 10. The heat exchanger according to claim 8 said at least onecurved heat exchanger plate (3, 3C, 3F, 103) is equipped with aplurality of second fins (32) in contact with said coolant (5, 5C, 5F,105).
 11. The heat exchanger according to claim 9, wherein said at leastone curved heat exchanger plate (3, 3C, 3F, 103) is equipped with aplurality of second fins (32) in contact with said coolant (5, 5C, 5F,105).
 12. The heat exchanger according to claim 10, wherein saidplurality of tubular elements or cores (1, 101) is parallel to eachother.
 13. The heat exchanger according to claim 12 wherein saidplurality of tubular elements or cores (1, 101) are held together bymeans of at least one strap, each clamping a tubular element andattached to a threaded rod (7) located between at least two of saidplurality of tubular elements or cores (1, 101).
 14. The heat exchangeraccording claim 12 wherein said plurality of tubular elements or cores(1, 101) are held together by means of at least one straps, eachclamping a tubular element and welded to each other.
 15. The heatexchanger according claim 12 wherein said plurality of tubular elementsor cores (1, 101) are held together by means of at least one strap, eachclamping a tubular element and soldered to each other.
 16. The heatexchanger according claim 12 wherein each tubular element or core (1,101) also comprises coolant conduits (8, 9, 108, 109) and spray nozzles(12, 13, 112, 113) that are adapted for spraying said coolant fromcoolant conduits (8, 9, 108, 109) onto said at least one curved heatexchanger plate (3, 3C, 3F, 103).
 17. The heat exchanger according claim16 further comprising: a pump having a pumping piston adapted foractuating a control means via a movement of a fluid; a drive pistonconnected by kinematic means to said pumping piston and adapted to beingactuated by said movement of said liquid (4, 104) of said heatexchanger; a hot source, and a cold source.
 18. The heat exchangeraccording to claim 17 wherein said pump further includes a bypassadapted for alternately feeding said coolant (5, 5C, 5F, 105) heatedunder pressure by said hot source and a coolant cooled at atmosphericpressure by said cold source into said plurality of tubular elements orcores (1, 101) of said heat exchanger.
 19. The heat exchanger accordingto claim 17 that includes said pump, a fluid reservoir and said controlmeans.
 20. The heat exchanger according to claim 18 that includes saidpump, a fluid reservoir and said control means.